WO2002007227A1

WO2002007227A1 - Light-receiving device and photodetector comprising light-receiving device

Info

Publication number: WO2002007227A1
Application number: PCT/JP2001/005963
Authority: WO
Inventors: Takashi Tagami; Kenichi Nakama
Original assignee: Nippon Sheet Glass Co., Ltd.
Priority date: 2000-07-18
Filing date: 2001-07-10
Publication date: 2002-01-24
Also published as: TW503587B; EP1233459A1; CA2385084A1; KR20020037050A; CN1383581A; US7372124B2; JP2002033507A; US20020149014A1; US20050058454A1

Abstract

A light receiving device for readily determining the center of gravity of the light intensity in a long wavelength band for optical communication. An InGaAs layer (i layer) and a p-type InP layer are formed on an n-type InP substrate, and electrodes are formed on the rear surface of the n-type substrate and at the opposite ends on the surface of the p-type layer. A spot light impinging on the surface is transduced photoelectrically to generate a photocurrent flowing laterally on the surface of the p-type layer, and a current corresponding to the distance is outputted from the electrodes at the opposite ends. The center of gravity of the light intensity is determined by calculation based on the values of the currents outputted from the electrodes at the opposite ends, and the light intensity is determined from the sum of the currents outputted from the electrodes at the opposite ends. Furthermore, a photodetector for measuring the light intensity and the center of gravity of each light produced by demultiplexing a wavelength multiplexed signal light is constituted using the light receiving device.

Description

Specification

Photodetectors and photodetectors using photodetectors

The present invention provides a light-receiving element that can continuously detect light intensity and the position of the center of gravity of a spectrum in a long wavelength band (for example, a 1.3 to 5.55 m band) used in the optical communication field. The present invention also relates to a photodetector using such a light receiving element, and further to an optical demultiplexer using the photodetector. Background technology

As an optical demultiplexer, the light condensed by a condenser lens is reflected by a mirror, the reflected light is demultiplexed by a diffraction grating, and the demultiplexed light is detected by a photodetector. An instrument is known (for example, a polychrome overnight photometric system sold by Shimadzu Corporation, model number PSS—100). The photodetector used in the optical demultiplexer is a light receiving element array, and is used as a spectrum monitor of the wavelength.

In such a photodetector, the spectrum of one wavelength is divided by a plurality of (for example, five) light receiving elements, and the position of the center of gravity of the light intensity is monitored. Determined by pitch. As described above, only a resolution corresponding to the arrangement pitch of the light receiving elements can be obtained, so that it was difficult to further improve the resolution with the conventional photodetector. The position of the center of gravity of the light intensity refers to the position of the center of gravity of the spectrum distribution because the signal light of each wavelength has a spectrum distribution. To cope with such a problem, we considered using a semiconductor position detector that can detect the position of the light spot as the light receiving element of the detector of the optical demultiplexer. This is because the semiconductor position detector is a non-segmented element, unlike the above-described light receiving element array, and therefore can continuously detect the position of the center of gravity of the light intensity in a spatially continuous manner.

As a conventional semiconductor position detector, the surface of a high-resistance Si substrate (i-layer) It is known that a P-type resistance layer is provided, an n-type layer is provided on the back surface, and an opposing electrode is provided on the p-type resistance layer.

In such a semiconductor position detector, since the surface layer forms a pn junction, when light enters the P-type resistance layer, a photocurrent is generated by the photoelectric effect. Since the photocurrent generated at the light incident position is divided so as to be inversely proportional to the resistance value to each electrode, the light incident position can be detected by the current extracted from each electrode.

The conventional semiconductor position detector uses the Si substrate as described above. However, semiconductor position detectors using Si substrates have poor sensitivity in the long wavelength band for optical communication. Therefore, when a conventional semiconductor position detector is used as the light receiving element of the optical demultiplexer, it is difficult to detect the position of the center of gravity of the light intensity for light in a long wavelength band. Disclosure of the invention

An object of the present invention is to provide a light receiving element used for a photodetector of an optical demultiplexer, which can easily detect the position of the center of gravity of light intensity in a long wavelength band for optical communication. It is here.

Another object of the present invention is to provide a photodetector of an optical demultiplexer using such a light receiving element.

Still another object of the present invention is to provide an optical demultiplexer using such a photodetector, which has improved resolution.

According to the present invention, as a light receiving element, in order to monitor a spectrum in a long wavelength band (for example, 1.55 m band) for optical communication, a III-V group having good sensitivity in a long wavelength band. A semiconductor position detector made of a semiconductor compound material is used.

A first aspect of the present invention is a light-receiving element, comprising: a layer made of a group III-V compound semiconductor; a first conductivity type resistive layer provided on a surface of the layer; A second conductivity type substrate opposite to the first conductivity type provided on the back surface; and a few opposed faces provided on the resistance layer. And a pair of electrodes.

A second aspect of the present invention is a photodetector for detecting the intensity of each demultiplexed light demultiplexed from a signal light in which a plurality of wavelengths are multiplexed and the position of its center of gravity. An array of one or more light receiving elements can be used.

A third aspect of the present invention is an optical demultiplexer that demultiplexes a signal light that has been wavelength-division multiplexed and transmitted, the optical means for demultiplexing the signal light, and the demultiplexed light demultiplexed by the optical means. And a photodetector for receiving light. For this photodetector, a photodetector configured by arranging the aforementioned light receiving elements is used.

FIG. 1A is a plan view showing one embodiment of the light receiving element of the present invention for monitoring one wavelength.

FIG. 1B is a cross-sectional view taken along the line XY of FIG. 1A.

FIG. 2 is a diagram showing a configuration of a circuit for performing position measurement using an output current from a light receiving element.

FIG. 3 is a diagram showing a time-division driving type photodetector.

FIG. 4 is a diagram illustrating a photodetector that detects the intensity of the demultiplexed light and the position of the center of gravity thereof.

FIG. 5 is a plan view of the photodetector shown in FIG.

FIG. 6 is a diagram illustrating another example of the photodetector that detects the intensity of the demultiplexed light and the position of the center of gravity.

FIG. 7 is a diagram showing one embodiment of the optical demultiplexer of the present invention.

Fig. 8 is a diagram for explaining the configuration for detecting the center of gravity of the light intensity of each of the k wavelengths of the C band and the k ₂ wavelengths of the L band. FIG. 4 is a diagram showing an example in which the same number of light receiving elements are integrated in two rows on a semiconductor chip. BEST MODE FOR CARRYING OUT THE INVENTION

Example 1

1A and 1B show a light-receiving element 8 for monitoring one wavelength, which is an embodiment of the light-receiving element of the present invention. 1A is a plan view, and FIG. 1B is a cross-sectional view taken along the line XY of FIG. 1A. According to the light receiving element 8, an InGaAs layer (i-layer) 12 and a p-type InP layer 14 are laminated on an n-type InP substrate 10. Electrodes 16 _a and 16 _¾ are formed on both ends of the surface of the p-type layer 14, and electrodes (not shown) are formed on the back surface of the n-type substrate 10.

The basic operation of the light receiving element 8 will be described. Supodzu bets light incident on the surface of the light receiving element is photoelectrically converted, so flows toward the surface of the p-type layer 1 4 to electrodes 1 6 _a, 1 6 _b photocurrent, current corresponding to the distance electrode output from the 1 6 _a, 1 6 _b. Photocurrent I generated at the incident position of the light is split so as inversely proportional to the resistance value to each of the electrodes 1 6 _a, 1 6 _b. The distance between the electrodes 1 6 _a, 1 6 _b to L _ab, the distance to the entrance position of the light from the electrode 1 6 _a a L _a.

If the resistance of the P-type layer 1 4 is uniform, the electrode 1 6 _a, 1 current from 6 _{_b} I _a, I _b is expressed by the following equation.

I _a = IX (L _ab -L _a ) / L _ab (1)

I b = I-^ L _a / 1 (2)

Here, when the ratio of the currents I _a and I _b or the ratio of the sum and the difference is obtained,

A I b 2 LL _a ― 1 (3)

_{_{(I a - I b) /}} (I a + I b)

= 1-(2 L _a / L ab) (4)

Is obtained. Thus, current I _a, the ratio of I _b or the ratio of the sum and difference, the light intensity and independent of the value in the variation.

Therefore, it is the this to obtain the (3) or (4) of if the ratio of the left side is possible measured, the distance L _a. Therefore, accurate position detection of incident light can be performed irrespective of a change in light intensity.

In the light receiving element of the present embodiment, I n having high sensitivity in a long wavelength band for optical communication is used. Since a GaAs-based material is used, high-sensitivity position detection is possible even in a long wavelength band, where the sensitivity of the conventional Si-based system is insufficient. Examples of InGaAs-based materials include III-V compound semiconductors such as GaAs, AlGaAs, InAs, InGaAsP, and the like. Can also be used. In the infrared region, Ge can also be used. Further, since the sum of the currents I _a and I _b becomes photocurrent I, the intensity of the incident light from the optical current I can be monitored.

Figure 2 shows a block diagram of a circuit which performs position measurement using a岀Ka current I _a and I _b from the electrode 1 6 _a, 1 6 _b of the light receiving element 8. After amplifying the output current I _a and I _b in preamp 1, 2, adder 3, performs addition and subtraction by the subtracter 4, divided by the divider _{_{5 (I a - I b)}} / (I a + I _{When b} ) is obtained, the light incident position can be measured from equation (4).

Note that FIG. 2 is shown a method of detecting in (4), (3) and this for obtaining the division I _a / I _b by equation Ru can light incidence position also measuring child.

Example 2

An example of a time-division driven photodetector that divides N time-division multiplexed signal light into N light using a diffraction grating and detects the position and intensity of each center of gravity will be described. .

FIG. 3 shows a photodetector 20 for monitoring such demultiplexed N wavelengths i, λ ₂ ,..., Λ _} . The structure of the photodetector 20 is basically the same as the structure of the light receiving element 8 shown in FIG. 1, but the light receiving section is configured to be large in order to receive all the demultiplexed light. It has been. In FIG. 3, a signal light containing Ν time-divided wavelengths is split into Ν pieces by a diffraction grating 22. People i, human ₂ wavelengths respectively, ..., demultiplexed light of e _N is incident on the photodetector 2 0.

Since the demultiplexed light is incident on the photodetector 20 in a time-division manner, the photodetector is driven by dividing the time into N pieces according to the timing of the incidence of the demultiplexed light. In this way, the respective light intensity centroids of the N demultiplexed lights are Can be detected. In addition, the intensities of the N demultiplexed lights can be detected from the respective photocurrents as described in FIG.

Example 3

An example of a photodetector that divides signal light in which N wavelengths are multiplexed into N light by a diffraction grating and detects the intensity of each divided light and the position of its center of gravity will be described.

FIG. 4 shows the photodetector 30 for monitoring the demultiplexed N wavelengths, person ₂ ,..., Λ _} . This photodetector 30 is composed of 受光 light receiving elements, D ₂ ,..., D _N arranged one-dimensionally. Each light receiving element is the light receiving element described in FIG. FIG. 5 shows a plan view of the photodetector 30. Each light receiving element, the electrode 1 6 _a, 1 6 _b are arranged side by side in the arrangement direction.

According to the present embodiment, the signal light including N wavelengths is split into N light beams by the diffraction grating 22 and is incident on the N light receiving elements, respectively. The position of the center of gravity can be detected. In addition, the intensity of each of the N pieces of demultiplexed light is detected from the photocurrent of each light receiving element as described in FIG.

Example 4

A signal light in which N wavelengths are multiplexed is demultiplexed into N light by a diffraction grating or the like. Another example of a photodetector that detects the intensity of each demultiplexed light and the position of its center of gravity will be described.

FIG. 6 is a diagram for explaining this photodetector. In this photodetector, the signal light is split into two by a half mirror 40, and one signal light is split into N by a diffraction grating 42, and the position of the center of gravity of each light intensity is shown in Fig. 5. Detection is performed by the first photodetector 30 described. The other separated signal light is split into N beams by the diffraction grating 44, and is divided into N photo diodes に Γ ^, PD ₂ ,…, PD _N arranged at each focal position. The second light detector 46 detects the intensities of the N branched lights.

In this embodiment, the second light detector 46 is more than the first light detector 30. Since the light receiving part can be made small, noise can be reduced and it is suitable for detecting the intensity of weak incident light.

Example 5

An embodiment of the optical demultiplexer of the present invention using the photodetector of Embodiment 2 or Embodiment 3 will be described. Fig. 7 shows an optical communication system of the wavelength division multiplexing transmission system, in which the wavelength division multiplexed light is demultiplexed for each wavelength at the receiving side, and the light intensity of each demultiplexed light and the position of its center of gravity are detected. The available optical splitters are shown. This optical demultiplexer is composed of one input fiber 50, a collimator lens 52, a diffraction grating 54, and a photodetector 56. Assembled using tubular members. The input fiber 50 is fixed to the fiber fixing window 60 on the end face of the transparent fiber mounting tube 58 by a fiber connecting portion 62. The lens 52 is fixed to the end of the intermediate tube 64. Further, the diffraction grating 54 is fixed to a diffraction grating fixing window 68 on the end face of the diffraction grating mounting tube 66. In this example, a fiber mounting tube 58 and a diffraction grating mounting tube 66 are provided at both ends of the intermediate tube 64 so as to be movable in the optical axis direction and rotate around the optical axis. Activate alignment is possible as much as possible.

In the optical demultiplexer having such a configuration, the light from the input fiber 50 is demultiplexed by the diffraction grating 54 through the collimator lens 52 and then collimated again. The light converged through the lens 52 is detected by the photodetector 56.

As described in Embodiments 2 and 3, the photodetector 56 can detect the position of the light intensity center of gravity of the demultiplexed light and the incident intensity of the demultiplexed light. Like a detector, the light that has been wavelength-division multiplexed is split into two by a half mirror, the position of the light intensity center of gravity is determined by the first photodetector 30, and A configuration for detecting light intensity can also be used. Example 6

8, in an optical communication system, light wavelength is multiplexed ki pieces of C-band (ki is an integer of 1 or more) the wavelength of the _two k of L-band (k ₂ is an integer of 1 or more) Is divided into ki band C and k node L ₂ by the diffraction grating 70, and the first photodetector composed of ki band light receiving elements for the C band (Not shown) and a _second photodetector (not shown) consisting of k band receiving elements for the L band, the light intensity centroid position of each of the (kt + ks) demultiplexed lights is determined. To detect.

If the first photodetector for the C band and the second photodetector for the L band are provided on separate semiconductor chips, it is difficult to match the relative positions and parallelism between the semiconductor chips with high accuracy Therefore, it is preferable to integrate them on a single semiconductor chip. By appropriately selecting the angles at which the C-band light and the L-band light enter the diffraction grating 70, the demultiplexed light of the C-band and L-band can be condensed into two adjacent rows. it can. The first and second photodetectors arranged in two rows are installed at the focusing position. Here, the light in the C band enters the diffraction grating at an angle closer to the normal direction of the diffraction grating than the light in the L band.

The number of light receiving elements to be installed on one semiconductor chip is k! The number is not limited to two and k ₂ for L band, and the same number may be provided in two rows. For example, place the ki-number of light receiving elements in two rows during ki ≥ k _2, when _two ≤k is disposed k ₂ pieces of light receiving elements in two rows, the light receiving element of x 2 columns or k ₂ X 2 rows of light receiving elements are formed on one semiconductor chip. FIG. 9 shows an example in which the same number of light receiving elements 8 are integrated in two rows on one semiconductor chip 72.

In the present embodiment, two bands, the C band and the L band, have been described. However, for light consisting of k bands, k rows of light receiving elements are arranged two-dimensionally. Thus, the demultiplexed light is detected.

The photodetector having such a configuration can be used for the optical demultiplexer shown in FIG. Industrial applicability

According to the present invention, since the light receiving element is made of a III-V compound semiconductor material having high sensitivity in a long wavelength band, it can be used for a long wavelength band spectrum used in the optical communication field. The intensity and its center of gravity can be detected continuously. Therefore, the resolution can be improved as compared with the conventional light receiving element. Further, according to the present invention, a photodetector using such a light receiving element can be realized, and further, by using such a light detector. Therefore, an optical demultiplexer having excellent resolution can be realized.

Claims

The scope of the claims

1. A light-receiving element that detects the light intensity of the light in the long wavelength band and the position of the center of gravity,

A layer composed of a III-V compound semiconductor;

A first conductivity type resistance layer provided on the surface of the layer,

A second conductivity type substrate provided on the back surface of the layer and having a conductivity type opposite to the first conductivity type;

A light-receiving element, comprising: at least a pair of electrodes facing each other provided on the resistance layer.

2. The III-V compound semiconductor is selected from the group consisting of InGaAs, GaAs, AlGaAs, InAs, and InGaAsP. The light receiving element according to claim 1, wherein

3. The light receiving device according to claim 2, wherein the III-V compound semiconductor is InGaAs. .

4. When the first conductivity type is p-type and the second conductivity type is n-type, the resistance layer of the first conductivity type is a p-type ΙηΡ layer; 4. The light receiving element according to claim 3, wherein the conductive type substrate is an η type In I substrate.

5. In a photodetector that detects the intensity of each demultiplexed light demultiplexed from signal light in which N time-division multiplexed wavelengths (N is an integer of 2 or more) and the position of the center of gravity,

A single light receiving element according to any one of claims 1 to 4, wherein the light receiving element is driven by dividing the time into N in accordance with the timing of the incidence of each demultiplexed light. A photodetector.

6. In a photodetector that detects the intensity of each demultiplexed light demultiplexed from the signal light in which N wavelengths (N is an integer of 2 or more) and the center of gravity thereof,

A photodetector, wherein the N light-receiving elements according to any one of claims 1 to 4 are arranged one-dimensionally.

7. In a photodetector that detects the intensity of each demultiplexed light demultiplexed from the signal light in which N wavelengths (N is an integer of 2 or more) and the position of the center of gravity,

The N light-receiving elements according to any one of claims 1 to 4, further comprising a first light detection unit arranged one-dimensionally, and wherein the first light detection unit detects a light intensity of each demultiplexed light. Detect the center of gravity position,

A second light detection unit in which N light receiving elements are arranged in a one-dimensional manner, the second light detection unit detects the light intensity of each demultiplexed light,

A photodetector, characterized in that:

8. The photodetector according to claim 7, wherein the light receiving element of the second photodetector is a photo diode.

9. A photodetector for detecting the intensity of each demultiplexed light demultiplexed from a signal light in which a plurality of bands including a plurality of wavelengths are multiplexed and the position of the center of gravity thereof, wherein the photodetector according to any one of claims 1 to 4 A photodetector, characterized in that a plurality of the light receiving elements described above are arranged one-dimensionally for each band.

10. An optical demultiplexer that demultiplexes signal light that has been wavelength-multiplexed transmitted, wherein: an optical unit that demultiplexes the incident light;

The light detector according to claim 5, which receives the demultiplexed light demultiplexed by the optical unit,

An optical demultiplexer comprising:

11. An optical demultiplexer that demultiplexes the signal light that has been wavelength-multiplexed transmitted, and an optical unit that demultiplexes the incident light.

The light detector according to claim 6, which receives the demultiplexed light demultiplexed by the optical unit,

An optical demultiplexer comprising:

12. An optical demultiplexer that demultiplexes the signal light that has been wavelength-multiplexed transmitted, and an optical unit that separates the incident light into two.

A first optical unit that splits the one of the separated incident lights, a second optical unit that splits the other of the separated incident light, and a splitter that is split by the first optical unit. The light detector according to claim 6, wherein the light detector receives the wave light, and detects a light intensity centroid position of each demultiplexed light.

A light-receiving element array that receives the demultiplexed light demultiplexed by the second optical unit and detects the light intensity of each demultiplexed light;

An optical demultiplexer comprising:

13. The optical duplexer according to claim 12, wherein the light receiving element array is a photodiode array.

1 4. In an optical demultiplexer that demultiplexes signal light in which multiple bands containing multiple wavelengths are multiplexed.

7. An optical unit for splitting the incident light into split light for each band, and a light receiving unit for receiving the split light for each band, wherein a plurality of photodetectors according to claim 6 are arranged.

An optical demultiplexer comprising: